1. Field of the Invention
The invention concerns a hydraulic switching system with an adjustable hydraulic pump in operative connection with at least one hydraulic energy consumer. A multiway valve is connected to the pump and to the hydraulic energy consumer. A pump regulating unit that can be loaded with pump pressure through a load-sensing regulator is connected to a control pressure line that is also connected with the hydraulic energy consumer.
Such a switching arrangement is known as load-sensing regulation. Load-sensing regulation induces delivery volume adjustment of the pump as a function of the hydraulic energy required by the hydraulic energy consumer. Thus, only the amount of hydraulic fluid actually required is delivered by the pump thereby avoiding unnecessary by-pass and throttling losses. If a hydraulic energy consumer is not actuated because the multiway valve assigned to it is in the zero or blocking position, the pump delivers only waste oil and is in a setting with only a small delivery volume, in which case the magnitude of the delivery pressure is determined by a governor spring that acts on a load-sensing regulator. The load-sensing regulator is a two-position/three-way valve having two control pressure chambers. One control pressure chamber is loaded by pump pressure and the opposite chamber is loaded by the pressure of the hydraulic energy consumer and by a governor spring which, for example, is designed so that the spring force coming from it corresponds to a pressure of 20 bar.
So long as no hydraulic energy consumer is actuated and the control pistons inside of the multiway valves assigned to the hydraulic energy consumers are in the zero position, the pump delivers only enough oil to maintain the pump pressure acting on the load-sensing regulator in equilibrium with the force of the spring that is acting on the opposite side of the load-sensing regulator.
By moving the control piston in a multiway valve located upstream of a hydraulic energy consumer, a connection is produced from the pump to the consumer so that the pump pressure is provided to the consumer. The port opened in the multiway valve through the movement of the control piston acts as a metering throttle. At the same time, the pressure at the hydraulic energy consumer, i.e., the pressure in the line between the multiway valve and the consumer loads the spring side of the load-sensing regulator through a control pressure line, so that the pump receives a signal to increase the delivery volume and thus the pump pressure increases. The hydraulic energy consumer is then set in motion and a pressure gradient, .DELTA.p, is produced at the metering throttle. Equilibrium is established in the system if the pressure gradient, .DELTA.p, in the multiway valve matches the spring pretensioning in the load-sensing regulator.
The pump delivery is thus automatically adapted to the pressure required. The multiway valve or its control piston for the hydraulic energy consumer is actuated through a hand lever, the adjustment path of which is proportional to the amount of hydraulic fluid reaching the hydraulic energy consumer, in which case the pressure gradient in the multiway valve always remains constant.
This system will function with a plurality of hydraulic energy consumers and load-sensing regulation as disclosed in U.S. Pat. No. 4,617,854 in which a pump loads a plurality of hydraulic energy consumers. A multiway valve with a built-in quantity regulator is located upstream of each consumer. An additional valve acting as a pressure regulator is built into the lines between the pump and the multiway valves. The pressure regulator control pressure chamber loading in the closing direction is created by the pressure in front of the multiway valve and its control pressure chamber loading in the opening direction is created by the pressure between the multiway valve and the hydraulic energy consumer inlet. An additional control pressure chamber acting in the closing direction is loaded by the pressure of the hydraulic energy consumer having the highest pressure and an additional control pressure chamber acting in the opening direction is loaded with the pressure in the delivery line from the pump.
The multiway valves with built-in quantity regulators distribute the pump stream load independently in relation to the throttle openings at the control piston so long as the stream delivered by the pump corresponds to the sum of the streams received by all of the consumers. If the sum of the consumer streams exceeds the maximum delivery stream of the pump, the maximum delivery stream is distributed to the consumers in the ratio in which the multiway valves assigned to the individual hydraulic energy consumers are opened.
When this system is used on dredges, for example, the path line of a dredge grab bucket produced by two simultaneously actuated operating cylinders is maintained and the rate with which the path line is traversed is reduced. A relatively large number of hydraulic energy consumers can be supplied with any amount of hydraulic fluid with no difficulty, in which case the working speed is substantially increased if all of the consumers are not simultaneously loaded.
A high working speed is, however, not desired in all of the working ranges of a dredge. It is necessary, especially in restricted space conditions, to actuate the hand levers connected with the multiway valves of the individual hydraulic energy consumers very carefully and not move them too vigorously. However, because only a limited adjustment path is available and a very great increase in performance or speed can be achieved within this adjustment path, a precise and delicate adjustment is very difficult and requires considerable concentration and experience by the dredge operator.